Hardenable polyurethanes are well known in the literature. U.S. Pat. No. 3,933,725, for example, describes the production of hardenable oligourethanes by the reaction of diphenylmethane di-isocyanates with polyoxypropylene diols and polyoxypropylene triols in a one-step process.
U.S. Pat. No. 3,707,521 describes the production of oligourethanes by the reaction of excess amounts of di-isocyanates with polyoxyalkylene groups still intact. These are reacted in a second step with diols to obtain products having isocyanate polyalkylene triols, forming a branched polyurethane, which still contains free isocyanate groups.
Products obtained according to the methods disclosed in these patents, or in similar ways, have the disadvantage that they harden with splitting of CO.sub.2. The hardening of moisture-reactive oligourethanes R--N.dbd.C.dbd.O may be illustrated approximately by the following reaction scheme: ##STR1##
Moisture hardening can lead to undesired bubble formation, while the hardening speed depends greatly on the humidity present in the air and is therefore difficult to control. The hardening takes place very slowly from the outermost layers inward, and not simultaneously in the whole mass, as in two-component products.
In the published German Patent Application No. 30 19 356 there is described the hardening of oligourethanes, containing isocyanate groups, with latent hardeners, for example, aldimines and oxaxolidines. Dienamines are also recommended as latent hardeners. Under these conditions, the rate of hardening, despite addition of the latent hardeners, still depends on the supply of moisture from the surroundings and the diffusion rate. Here also, the hardening takes place gradually from the outside to the inside and requires rather long times, expecially with thick layers.
Recommended blocking agents for isocyanate functions in polyurethanes are methylol ether, malonic acid ester, caprolactam, phenols and ketoximes. (See, in this regard, the published German Patent Application Nos. 29 46 085; 25 42 500; 25 50 156; and 29 29 224.) Hardening with blocking agents, however, has the disadvantage of requiring higher temperatures, at which volatile splitting products sometimes result, which can lead to bubble formation.
U.S. Pat. No. 3,054,755 describes a polyrurethane which results by reaction of a polyisocyanate with a polyalkylene glycol (poly-alkylene ether glycol) and subsequently with an amino alcohol. U.S. Pat. No. 3,228,914 describes the reaction of a prepolymer containing isocyanate groups with an amino alcohol. This material is finally hardened by addition of an aromatic di-isocyanate monomer at a raised temperature and under pressure. U.S. Pat. No. 3,114,734 describes compound which result by reaction of amino mercaptans and dimercaptans with terminal isocyanate groups of polyurethane resins. This material is vulcanized by oxidation of the mercapto groups.
The above-described two-component systems have the disadvantage that their components must generally be used in exact stoichiometric mixing proportions; otherwise, products result with greatly diiffering, often unsatisfactory physical properties, and the degree of hardening is left to chance. In cases where no stoichiometric mixing proportion is required it is generally a matter of low-molecular crosslinking agents. Here the hardening generally takes place so rapidly that handling is extremely difficult. Also, products result which often do not have the desired physical properties.